1. Field of the Invention
The invention relates to a keyboard apparatus, and more particularly, relates to a keyboard apparatus capable of avoiding misjudgment due to ghost key and a detection method for status of keys thereof.
2. Description of Related Art
Referring to FIG. 1, FIG. 1 is a schematic diagram of a conventional keyboard apparatus 100. The keyboard apparatus 100 includes keys SW1 to SW4 and comparators 10 and 20. The key SW1 is coupled between a driving line DL1 and a sensing line SL1. The key SW2 is coupled between the driving line DL1 and a sensing line SL2. The key SW3 is coupled between a driving line DL2 and the sensing line SL1. The key SW4 is coupled between the driving line DL2 and the sensing line SL2. The comparator 10 is coupled to the sensing line SL1 to receive a voltage signal SV1 and compares the voltage signal SV1 with a reference voltage Vref. Similarly, the comparator 20 is coupled to the sensing line SL2 to receive a voltage signal SV2 and compares the voltage signal SV2 with the reference voltage Vref.
During detection of a press status of the keys SW1 to SW4, the driving line DL1 may be driven to a voltage level and the driving line DL2 may be driven to another voltage level. When the driving line DL1 is driven to said voltage level, the keys SW1 and SW2 transmit the corresponding voltage signals SV1 and SV2 to the comparators 10 and 20 respectively through the sensing lines SL1 and SL2 according to the press status. Then, the voltage signals SV1 and SV2 are respectively compared with the reference voltage Vref by the comparators 10 and 20 so as to determine the press status of the keys SW1 and SW2. Similarly, when the driving line DL2 is driven to said another voltage level, the keys SW3 and SW4 transmit the corresponding voltage signals SV1 and SV2 to the comparators 10 and 20 respectively through the sensing lines SL1 and SL2 according to the press status. Then, the voltage signals SV1 and SV2 are respectively compared with the reference voltage Vref by the comparators 10 and 20 so as to determine the press status of the keys SW3 and SW4.
It should be noted that, when a number of the sensing lines is increased due to increasing number of the keys in the keyboard apparatus, a number of the comparators to be coupled to the sensing lines for comparing the voltages must also be increased. However, errors may occur on the comparators due to drifts in the manufacturing process and result in misjudgment of the press status of the keys. Therefore, a calibration must be performed on each of the comparators in order to obtain an offset of each of the comparators, so that the press status of the corresponding key may be precisely detected. Aforesaid detection method for status of keys tends to consume more circuitry resources since the offset of each of the comparators must be stored.
On the other hand, it is also possible to adopt use of only one comparator that is precisely calibrated, so that this precisely calibrated comparator may sequentially perform comparison for the voltage signal on one of the sensing lines. Nonetheless, such detection method for status of keys is unable to concurrently and parallelly perform comparison on the voltage signals on all the sensing lines, and thus a detection speed thereof is relatively slower.